Traditionally glycerin has been refined to make a 99.9% pure product for the USP market. The source for the glycerin came from either soap manufacturers or fat splitting. As biodiesel refineries started to come on line in the beginning of 2000, a new grade of crude glycerin started to become available. This product was around 50-80% pure and there was little to no market for it and it was considered a waste product of the biodiesel industry. Some larger refiners of biodiesel began to hire olechemical process engineering firms to design systems to upgrade the crude glycerin to a 99.9% pure product, but the expense of such systems would cost millions of dollars. This high cost of building a glycerin refinery resulted in only a few large scale refineries implementing glycerin refining into their production process. In order for smaller scale refineries below 100,000,000 gallons per year of biodiesel to consider building a glycerin refinery there needed to be a system that costs less and did not take up a large section of space since most refineries where utilizing most of their square feet for their production process. Also a new market needed to be developed that did not require a 99.9% pure glycerin. A technical market that could accept an 85-95% pure glycerin needed to be developed. Also a limiting factor was that it is more difficult to refine crude glycerin from biodiesel into 99.9% pure glycerin because of the unique contaminants that are present with the biodiesel based crude glycerin.
The crude glycerin from biodiesel is made as a coproduct from the transesterification of triglycerides into fatty acid alkyl esters. The three fatty acids are separated from the triglyceride leaving a glycerin molecule. This glycerin binds with residual sodium hydroxide or potassium hydroxide catalyst from the transesterification reaction and it also binds fatty acids that were attached to the sodium or potassium ion from the catalyst in the form of soaps. Any water that was in the triglycerides or water created from mixing up the catalyst also goes into the glycerin layer. Some partially reacted biodiesel and even some fully reacted biodiesel are also mixed with the glycerin as well as glycerides and finally 60% of the excess alcohol used in the transesterification reaction also mixes into the glycerin product. The result is a crude glycerin with fatty acids, mono- and di-glycerides, salts, soaps, alcohol, water, and some biodiesel. This creates a glycerin with around 50% purity.
There is public knowledge on the basic principles of purifying the crude glycerin from the biodiesel reaction. As discussed in the www.journeytoforever.org website under glycerin separation, glycerin is purified by adding phosphoric acid until the glycerin is neutral pH. It then splits into 3 layers. The top layer being fatty acids and biodiesel; the middle layer being glycerin, methanol, water and excess catalyst; and the bottom layer being salts and other solids. This basic method works. However, in order to eliminate the methanol to a level below 1%, which is a requirement for most customers of glycerin, this method is not sufficient.
Many prior patents relating to the purification of glycerin, such as U.S. Pat. Nos. 2,615,924, 2,741,638 and 2,772,207, are aimed at purifying glycerin from high percentages of water, such as those resulting from fermentation and hydrolysis. Whereas, U.S. Pat. No. 2,234,400 describes purification after concentrating the glycerin to a purity of 80% comprising one or more steam distillations followed by treatment with activated carbon or the like to remove color. Even then, the impurities found in glycerin from the biodiesel production process, such as alcohol, are not discussed.
U.S. Pat. No. 4,655,879 describes an approximately 10-step process comprising alkalizing in the presence of air, evaporating in a thin-film evaporator, redistillation of the residue, rectification in a low-pressure-drop column with reboiling in a falling-film evaporator, main product removal as a liquid sidestream, with carbon treatment for color removal.
In the references discussed in the preceding two paragraphs, methanol was not present, or not mentioned, as a constituent in the crude feed.
U.S. Pat. No. 7,126,032 mentions methanol as a constituent of the crude glycerin feed and it also mentions water from the waste stream of biodiesel production. The patent describes neutralizing the glycerin to pH 7. However, the process for purification utilizes different pieces of distillation equipment and the design relies on nitrogen gas. Furthermore, there are more steps involved in the process and the purity of glycerin produced is 99%. In contrast, in the process described in this application, the result is a technical grade glycerin ranging from 80-90% purity.
In summary, a new method of refining glycerin from the biodiesel refining process needs to be developed that takes up a small space and has a cost below $1,000,000. This would allow biodiesel refineries to have a sellable commodity glycerin into a technical market. The following invention solves these issues.